Material to absorb RF

Question

I need to put an antenna close to/against metal. What sort of material could I put below it to absorb the RF rather than the metal reflecting it? ...Skeeve

gervasi · Answer

What are you trying to accomplish? Ordinarily I'm trying to prevent objects near an antenna from absorbing energy from the antenna. Once you tell me your goal, I may realize I was missing an obvious inference that I failed to see. I have some thoughts about this once you tell me what you're trying do.

mcb1 · Answer

What sort of frequency are we talking about.?

many antenna designs use the metal ground to reflect the other half of the antenna, and a 1/4 wavelength does exactly that.

If the metal box is associated with the reader you may be able to utilise it for part of your antenna.

Rather than reflect the signal straight back into the antenna, I was hoping to absorb it to reduce conflicting noise.

If the antenna and the beacons are on similar frequencies, and you need to get a signal back to the reader, then you may have issues.

If the antenna is simply transmitting then it won't care about the beacons, even if it is on the same frequency.

Perhaps some added information might allow us to make some better suggestions.

Mark

gervasi · Answer

The antenna will be right against steel and aluminium. The antenna will be right against steel and aluminium. I think you should have the antenna not contact the aluminum, but it can be close. If possible bond the RF ground on the board to the aluminum enclosure, close to where the antenna protrudes. Then the aluminum of the enclosure will act as a ground plane for the antenna. Passing through the aluminum hole will affect impedance matching to the antenna, but hopefully not that much. You could find someone to match later as a finishing touch. It shouldn't be too much of a problem. Your signal will radiate outside the enclosure and have decent isolation from things inside the enclosure.

genebren · Answer

Hi Skeeve, I have not used these materials, but this might be what you are looking for: http://www.masttechnologies.com/rf-absorbers/ Good luck, Gene

jc2048 · Answer

If it's microwave (2.4GHz ISM or above) you might consider a patch antenna. That could sit against metal without any problems (internally, the patch is placed just above a ground plane, so further metal underneath doesn't affect the properties). You can buy commercial patch antennas with ceramic between the patch and the plane. Here's an example (not a recommendation - I've never used one of these) http://www.taoglas.com/product/wlp-2450-25-4-a-02-2-4ghz-bluetooth-wlan-zigbee-patch-antenna-25mm/

Material to absorb RF

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